Observed and Dark Diversity of Alien Plants Across the World

Aim: Biological invasions are one of the major threats to ecosystems worldwide and are expected to increase further in the future. Prevention and swift responses are crucial to mitigate this threat. However, predicting new alien species' arrivals remains a challenge. Here, we identified the distribution pattern of potential new invasion by defining regional alien dark diversity-ecologically suitable but currently absent sets of alien plant species. Location: Global. Time Period: Current and future. Major Taxa Studied: Plants. Methods: Applying a probabilistic approach based on the co-occurrence of over 346,000 species, we identified the size and composition of alien dark diversity in 367 regions. Using recognised invasion drivers, we assessed their effects on observed and alien dark diversity. Additionally, we used projected socioeconomic scenarios for 2050 and related them to the alien dark diversity, describing risks for future invasions. Results: Global distributions of alien observed and dark diversity sizes differed considerably. In contrast to alien observed diversity trends, alien dark diversity was higher in smaller, naturally species-poor, and unproductive dry regions. While alien observed diversity increased with economic wealth, dark diversity decreased. Urbanisation was the only variable where both alien biodiversity metrics showed a consistent positive relationship. By 2050, about a quarter of the globe's land area will face a high risk of future invasions, with the most suitable dark diversity species being shared between regions. Main Conclusions: We show that alien ecological suitability is enhanced by urbanisation, but GDP is one of the most important drivers of invasion, as it facilitates alien species' arrival. As many regions share similar potential new invaders, some with disruptive ecological roles, we highlight the importance of sharing invasion control strategies. Knowledge about alien dark diversity facilitates the assessment of forthcoming invasion risks, enabling preparation ahead of time for mitigating the adverse effects of biological invasions.